package com.wc.alorithm_blue_bridge_history.simulation_match3.I;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.PrintWriter;
import java.util.Arrays;
import java.util.StringTokenizer;

/**
 * @Author congge
 * @Date 2024/3/8 15:36
 * @description
 * https://www.lanqiao.cn/problems/16567/learning/?problem_list_id=29&page=1
 */
public class Main {
    static FastReader sc = new FastReader();
    static PrintWriter out = new PrintWriter(System.out);
    static int N = 1010;
    static char[][] a = new char[N][N];
    static int n, m;

    public static void main(String[] args) {
        n = sc.nextInt();
        m = sc.nextInt();
        a[0] = new char[m + 2];
        // 用空格包围
        Arrays.fill(a[0], ' ');
        for (int i = 1; i <= n; i++) a[i] = (" " + sc.next() + " ").toCharArray();
        int res = 0;
        // 遍历每一个中心点
        for (int i = 2; i <= n; i++) {
            if (Math.min(n - i, i - 1) <= res) continue;
            for (int j = 2; j <= m; j++) {
                //能形成的最大边界
                if (Math.min(j - 1, m - j) > res) {
                    // 字符都以这个为标准
                    char c = a[i][j];
                    int ux = i - 1;
                    int ly = j - 1;
                    int ry = j + 1;
                    int dx = i + 1;
                    int dy = j;
                    while (a[ux][ly] == c && a[ux][ry] == c && a[dx][dy] == c) {
                        dx++;
                        ux--;
                        ly--;
                        ry++;
                    }
                    res = Math.max(res, dx - i - 1);
                }
            }
        }
        out.println(res);
        out.flush();
    }
}

class FastReader {
    StringTokenizer st;
    BufferedReader br;

    FastReader() {
        br = new BufferedReader(new InputStreamReader(System.in));
    }

    String next() {
        while (st == null || !st.hasMoreElements()) {
            try {
                st = new StringTokenizer(br.readLine());
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
        return st.nextToken();
    }

    int nextInt() {
        return Integer.parseInt(next());
    }

    String nextLine() {
        String s = "";
        try {
            s = br.readLine();
        } catch (IOException e) {
            e.printStackTrace();
        }
        return s;
    }

    long nextLong() {
        return Long.parseLong(next());
    }

    double nextDouble() {
        return Double.parseDouble(next());
    }

    // 是否由下一个
    boolean hasNext() {
        while (st == null || !st.hasMoreTokens()) {
            try {
                String line = br.readLine();
                if (line == null)
                    return false;
                st = new StringTokenizer(line);
            } catch (IOException e) {
                throw new RuntimeException(e);
            }
        }
        return true;
    }
}